There have been many attempts to harness wave energy dating as far back as 1799. To date attempts have been unsuccessful in large measure because the investment and maintenance costs have been too high. It is exceedingly difficult to build a structure that will survive the salt water environment over a long period of time. The problem is difficult for three reasons. First, the energy in the waves can be as high as 1000 kw per meter in gales. Thus, a device designed for an average of 10 kw per meter will tear itself apart Second, if the device can survive the varying sea states, it must withstand the constant corrosive environment. Third, the device must not be adversely affected by marine growth.
A comparative survey of twelve wave energy conversion devices has been published in Hagerman and Heller, Wave Energy: A Survey of Twelve Near-Term Technologies. August 1988. The twelve devices have been grouped into five categories: heaving floats, heaving and pitching floats, pitching devices, oscillating water columns, and surge devices. The present invention falls under the first two categories.
Representative references showing known wave energy devices include Windle, U.S. Pat. No. 4,754,157; Liu et al., U.S. Pat. No. 4,081,962; Wood, U.S. Pat. No. 4,603,551; Hopfe, U.S. Pat. No. 4,335,576; and Menk, U.S. Pat. No. 4,185,947.
The more relevant reference is Windle which discloses a float type wave energy extraction apparatus and method. The apparatus comprises a cylinder with inlet and outlet check valves, a reciprocal piston in the cylinder, a piston rod connected to the piston and extending sealably out of the cylinder, a mechanical tensioning device connected between the piston and the cylinder for maintaining resilient tension between the piston and the cylinder, a float connected to a piston rod or the cylinder, and an anchor flexibly connected to the other of the piston rod or the cylinder which is not connected to the float. However, the present invention distinguishes over Windle, as will be described hereinafter.